The present invention more specifically relates to an alignment measuring device for wheels of an automotive vehicle or the like, by which the inclination angles, in particular the toe-in angle and the camber, of a wheel mounted through the suspension of the vehicle is measured in a contactless manner, namely by non-contact distance measurement with the stationary (not rotating) wheel.
In this application, the term “wheel” should be understood to include the hub, the spokes or disk of the wheel, and the rim, in particular the flange of the rim also called bead of the rim, at which the edge forms the border between the mounted tire. A wheel can be made of an applicable material, nowadays mostly an aluminum alloy. The part of the wheel on which a tire is mounted is the rim and the edges of the rim preventing the tire from getting off the rim are the bead of the rim. The middle of the wheel, where it normally is mounted to a vehicle's axis is the hub of the wheel. The portion between the hub and the rim can be spokes of or the disk of the wheel; the area where a spoke merges the rim is the spoke's base. In this context an automotive vehicle may be generally motor driven vehicle, a motorcycle, a car, a truck, or even an airplane the landing gear of which also having wheels. In other words, any kind of object with turning wheels, the wheels of which may be subject to the method or apparatus of the present application. The tire mounted to the wheel is sometimes also considered as part of the wheel, but for the purpose of adjusting the alignment of the wheels on the automotive vehicle or the like, the measurement of the alignment of the wheel itself is more reliable, since a tire may have irregularities.
According to the general aspect, correct alignment of the wheels of automotive vehicles requires measurement of the respective inclination angles indicating the mounting respective position of the wheels with respect to each other and the automotive vehicle. In this context, toe-in angle is the inclination angle of the wheel or the tire surface with respect to the direction of progress of the vehicle, the camber angle is the degree of inclination of the wheel or the tire surface with respect to the vertical plane, and the caster is the angle between the vertical at the wheel center and the inclination of the king pin shaft as viewed directly sideways from the wheel. Accurate measurement and an correct adjustment of the wheel alignment including all of these angles is the important factor for improving the driving characteristics of the respective vehicle, in particular with respect to the tire wear.
The toe-in angle indicates whether the tires are wider apart at the front or at the back as viewed from above the vehicle body and concerns both the front and rear wheels. If wheels are wider apart at the front, this is called toe-out, and if the wheels are wider apart at the rear, this is called toe-in. The camber angle indicates whether the wheel is wider apart at the top or at the bottom as viewed from the direct front or rear of the vehicle, and represents the angle formed by the normal to the ground contact point of the tire and a straight line along the tire. When the tire is perpendicular to the ground, the camber is zero; when the tire is inclined inward, the camber is negative; and the tire inclined outward is positive in camber. The camber angle is measured for the purpose of facilitating the steering operation, reducing the vertical load and preventing the wheel from becoming wider apart at the bottom. A positive caster is involved if the king pin shaft is inclined rearward, a negative caster is involved if the king pin shaft is inclined forward, and a zero caster is involved if the king pin shaft is in a vertical position. The caster is required for maintaining the straight-line stability.